1. Field of the Invention
The present invention relates to a method of removing gas or air bubbles from a liquid-containing cylinder chamber of a dosage piston pump, such as a piston burette.
2. Description of the Prior Art
Most liquids contain small amounts of air or gas in dissolved condition or in the form of small bubbles. Therefore, after a certain period of operation of burettes and other liquid dosage pumps greater or smaller air or gas bubbles may collect therein. Such air or gas bubbles are rather disadvantageous in liquid dosage piston pumps in which the metered amount of liquid is normally determined on the basis of the displacement movement of the piston. An air or gas bubble positioned within the cylinder space of the pump will to some extent expand during the suction stroke of the pump due to the reduced cylinder pressure, while the air bubble will become somewhat compressed during the pressure stroke. If part of the gas or air within the cylinder flows out therefrom together with the liquid during the pressure stroke the accuracy of the metering will be influenced in a disadvantageous manner, because the actual amount of liquid being pumped may be somewhat smaller than that determined on the basis of the piston movement. Furthermore, the resiliency of the air bubbles may cause that liquid continues to flow out from the cylinder a small period of time after termination of the pressure stroke, which is less convenient.
For the above reasons it is important that a dosage pump be vented at certain time intervals. When the cylinder of the dosage pump is positioned with a substantially vertical axis, venting of the cylinder may simply take place through a venting opening positioned at the upper point of the cylinder end wall and preferably above the points where the inlet and outlet conduits of the pump open into the cylinder space. When the cylinder is to be vented the normally closed venting opening is opened while the piston is moved upwardly, whereby possible air bubbles are removed from the cylinder space together with part of the liquid therein. For various reasons it may be desirable to arrange the dosage pump with a substantially horizontal cylinder axis. The pump may then be built into existing module cabinets together with appertaining accessory equipment in the form of driving and controlling devices, whereby the pump may be well protected and the pump and the accessory equipment belonging thereto may be given a more compact shape.
However, it has been found that it is much more difficult to vent the horizontally arranged cylinders of dosage pumps. Even when a venting opening has been formed in the upper part of the cylinder end wall the relatively small air bubbles in question will tend to adhere to the cylinder wall and the piston top, and when the piston is moved towards its top position it will be difficult to secure that all air bubbles flow out through the venting opening together with the liquid, because they often remain in the "dead space" of the pump when the piston has been moved to its top position. It has been proposed to remove the air bubbles by flushing the "dead space" with a liquid while the piston is in its top position. Such venting procedure is, however, relatively complicated and requires use of further accessory equipment for this flush process.